Fluid pump changeable in diameter, in particular for medical application

ABSTRACT

A fluid pump device changeable in diameter is provided. The device has a pump housing which is changeable in diameter and with a rotor which is changeable in diameter. The device has at least one delivery element for fluid, as well as a drive shaft on which the rotor is rotatably mounted. A bearing arrangement is arranged on the drive shaft or its extension, at the distal end of the drive shaft behind the rotor seen from the proximal end of the drive shaft. The bearing arrangement has struts, which elastically brace between a hub of the bearing arrangement and the pump housing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of pending U.S. patentapplication Ser. No. 15/281,796, filed Sep. 30, 2016 (now allowed),which is a continuation application of U.S. patent application Ser. No.14/576,396, filed Dec. 19, 2014 (now issued as U.S. Pat. No. 9,512,839),which is a continuation application of U.S. patent application Ser. No.13/318,678 filed Nov. 29, 2011 (now U.S. Pat. No. 8,944,748), which is a371 national stage filing of PCT International Application No.PCT/EP2010/002827, filed Apr. 29, 2010, which claims the benefit of U.S.Provisional Application No. 61/175,519, filed May 5, 2009, and EuropeanPatent Application 09075221.3, filed May 5, 2009, all of which arehereby incorporated by reference in their entireties. InternationalApplication No. PCT/EP2010/002827 was published under PCT Article 21(2)in English.

BACKGROUND OF THE INVENTION

The invention lies in the field of mechanics, in particular precisionmechanics, and may be advantageously applied to the medical field.

However, independently of the application in the medial sector,applications in other fields may be envisaged, where a fluid pump is tobe operated under restricted spatial conditions or at poorly accessiblelocations.

This is particularly the case with minimal-invasive medical technology,where often medical instruments or apparatus must be brought to thelocation of application, for example through blood vessels, with an asgentle as possible treatment of the patient. It is particularly in thiscontext that the application of blood pumps in combination withcatheters has become known, which for example may be introduced into aheart chamber whilst supporting the heart pumping activity.

Since a certain size is necessary for an optimised performance of such apump, which however is limited by the diameter of the large bloodvessels of the body which end in the heart, it is already known to usefluid pumps which are changeable in their radius for this purpose, whichmay be expanded after introduction into the heart chamber.

BRIEF SUMMARY OF THE INVENTION

This is made possible either by way of special mechanisms, which permitan actuation of a spanning mechanism of the pump by way of a catheter,as is known for example from the US patent document US 2008/0103591 orWO 03/103745, or by way of the use of so-called memory materials, whichmay assume different shapes when changing the temperature of thesurroundings, and may be brought into the desired end shape by way oftemperature change.

An alternative solution is known from U.S. Pat. No. 7,393,181 B2, withwhich flexible rotor blades may be applied onto a hub and be reversiblydeformable in a manner such that they are automatically set up on pumpoperation.

However, tight limits are placed on the expansion ability of such pumpsdue to the necessity of accommodating a drive shaft as well as a rotorand pump housing within a small diameter.

In this context, it is the object of the present invention to create afluid pump, which with as little as possible design effort, permits anas simple and as large as possible changeability of the diameter.

According to the invention, this object is achieved by the features ofpatent claim 1.

Thereby, a pump housing which is changeable in diameter as well as, asthe case may be, also a rotor changeable in diameter, is provided withat least one delivery element for the fluid, as well as an actuationmeans, in particular a pull means, at whose end which is distal seenfrom the introduction location of the catheter, the fluid pump isarranged.

The actuation means is displaceable in a longitudinal direction. Thepump housing and the rotor are displaceable relative to one another tosuch an extent in the longitudinal direction of the actuation means byway of the actuation means, that they may be arranged behind one anotherin the longitudinal direction, or with a mutual overlapping in thelongitudinal direction, which is smaller than the overlapping during theoperation of the fluid pump, in order to permit an efficient compressionto a smaller diameter. This may be realised by way of either the pumphousing or the rotor or both being displaceable with respect to theactuation means. In this context, the pump housing is to be understoodas that in which the rotor is located and rotates, preferably withoutwall contact, during pump operation.

Thus the rotor may be moved at least partly out of the pump housing foran efficient compression of the rotor. The compression movement of thepump housing is then not limited by the rotor, which is completelyaccommodated in it.

One may also envisage the actuation means between the distal end and theproximal end at least in sections running in a sleeve or parallel to asleeve. It is however also possible for the actuation means to runparallel to another guide means, for example a guide wire, and for nosleeve to be provided.

The actuation means may for example be used as a pull means and bedesigned as a drive shaft, at whose proximal end a rotation drive forthe pump is provided. The drive shaft in this case is rotatable andfurthermore displaceable in the longitudinal direction.

Apart from this embodiment, there is also the possibility of driving thepump by way of an implantable miniature motor which is arranged at thedistal end of a sleeve or another guide means, and which is implantableinto the body, or also a hydraulic microturbine. Instead of the driveshaft, the fluid pump then has its own actuation means, such as forexample a cable or a wire or likewise, which displaces the rotor orother parts of the pump, in particular also pulls a bearing arrangementinto the pump housing.

Furthermore, in the first mentioned case, there is also the possibilityof applying a more suitable pull means additionally to a drive shaft.This permits the drive shaft to be optimised with regard to the demandsconcerning the torque transmission and running time, and permits thepull means to be optimised independently of this, with regard to thepulling function.

Such a pull means may for example be a cable of plastic or a wire cableor also a wire or any other suitable pull means. In the case of the useof an implantable miniature electric motor, one could for example alsouse the cable necessary for operation of the motor, as a pull means, andin the case of the use of a hydraulic microturbine, the hydraulicconduits or flexible tubing required for the operation of this turbinemay also be used as pull means.

If the actuation means is stiff enough, for example is designed as wire,then a push movement may also be designed in a controlled manner. Withthis for example, the pump housing may also be pushed to the rotor inthe longitudinal direction of the actuation means.

The pump housing may for example consist of an elastic framework, e.g.of a memory alloy or of a plastic, which is coated with a membrane, forexample of polyurethane. The pump housing on the other hand may howeveralso consist of segments which are moveable to one another, such as e.g.scales or lamellae which as a whole are movable and may be compressed,wherein individual scales/segments or lamellae may be stiff per se orflexible. The rotor, as the case may be, is compressible per se by wayof the fact that either individual delivery elements of the rotor may befolded or pivoted onto the shaft for reducing the diameter, or the factthat the rotor consists of a membrane which may be stretched out by wayof one or more tautening elements.

Additionally to the outlined embodiments of the pump housing and therotor, also other compressible and expandable construction shapes areconceivable for the application of the invention.

It is advantageous for a particularly good compressibility of thearrangement, if the pump housing and the rotor are displaceable to oneanother so far in the longitudinal direction of the actuation means,that they may be arranged behind one another in the longitudinaldirection, or with a mutual overlapping in the longitudinal direction,which is smaller than the overlapping during the operation of the fluidpump. The different parts thereby may be displaceable on a drive shaft,which either forms the actuation means or whose extension is in theregion of the pump, if an implantable miniature motor is provided at theend of the sleeve.

A particularly advantageous embodiment of the invention envisages abearing arrangement being arranged on the actuation means or itsextension, at the distal end of the actuation means or its extension,behind the rotor seen from the rotation drive.

One achieves a particularly quiet and smooth running of the rotor by wayof a further mounting at the distal end of the pump housing beingprovided additionally to a mounting at the proximal end of the pumphousing. The respective bearing arrangement may likewise be movablerelative to the pump housing within the framework of the invention. Itis advantageously displaceable on the actuation means or its extension,in their longitudinal directions, or at least displaceable with theactuation means or the extension, with respect to the rotor and the pumphousing, as long as the actuation means itself is displaceable in thelongitudinal direction.

After the expansion of the fluid pump device, the bearing arrangementmay be brought by way of this to its location of application at thedistal end of the pump housing, by way of a further displacementmovement.

A further advantageous design of the invention envisages the bearingarrangement being displaceable relative to the rotor in the longitudinaldirection of the actuation means.

With this, the bearing arrangement as well as the rotor may becompressed and expanded independently of one another and be displaced toone another in the longitudinal direction only after the attachment ofthe fluid pump device, in order to achieve the operating arrangement.

If the bearing arrangement is axially displaceable to the actuationmeans or the extension, then an abutment body should be provided onthese, for example at their end which on pulling back the actuationmeans, entrains the bearing arrangement in the direction of theactivation device.

The bearing arrangement for its part may then abut against the rotor andalso move this in the direction of the pump housing up to the endposition.

One may also envisage the bearing arrangement being movable with therotor into the inside of the pump housing, and struts arranged in astar-like manner being provided, which elastically brace between a hubof the bearing arrangement and the pump housing.

This may advantageously be achieved by way of the struts beingelastically pivotably fastened on the hub of the bearing arrangement.

For this purpose, the struts just as the bearing arrangement, may forexample consist of an elastic plastic or rubber, or of a spring-elasticmetal.

It may also be advantageous for the struts to be radially extended byway of folding open in the course of the movement of the drive shaft, byway of axial compression of the bearing arrangement. This e.g. ispossible if the bearing arrangement comprises two rings which aremutually to one another in the axial direction, between which the strutsare fastened, wherein the struts bear in a flat manner given a largerdistance of the rings, and are expanded in a bead-like manner with apushing-together of the rings.

The struts in the braced condition may advantageously form an inflowcage at the distal end of the fluid pump, which on the one hand preventsthe rotor from coming into contact with body tissue and one the otherhand ensures that any larger coagulated masses, which are located in thefluid to be delivered, may not penetrate into the pump housing.

Moreover, it is advantageous to design the actuation means in adisplaceable manner with respect to the sleeve in the longitudinaldirection, in particular to the rotation drive at the proximal end ofthe sleeve, in order to effect the different axial displacementmovements of the pump housing, the rotor and the bearing arrangement toone another.

The sleeve thereby is usually designed as a catheter in the field of themedical application. Such a catheter although being flexible, is also sostiff that it may be pushed through a blood vessel. The catheter isusually connected to the pump housing in a fluid-tight manner, whereinthe actuation means, for example a drive shaft, is introduced in an assealed as possible manner into the pump housing through a rotationlead-through.

The catheter, at the proximal end which usually lies outside the body ofthe patient, is connected in a fluid-tight manner to an actuation deviceand for example also to an electromotoric drive, inasmuch as noimplanted micro-motor is preferred in the region of the fluid pump.

Advantageously, the catheter is filled with a body-compatible fluid, forexample a saline solution, in order on the one hand to prevent thepenetration of gas bubbles into the body and on the other hand, as thecase may be to lubricate and cool the shaft which usually rotates at20,000-35,000 revolutions per minute.

The present invention in the case that it is provided within the sleeveof a drive shaft, may further advantageously be designed such that thedrive-side end of the drive shaft is connected to a drive body which isarranged in a sealed housing and which may be driven in a magnetic androtatory manner from outside the housing.

This embodiment permits the drive of the drive shaft through amagnetically inactive housing, without a rotation lead-through which isto be sealed off, by way of a rotation field being applied, which setsthe drive body located in the housing and thus the drive shaft, intorotation.

A displacement ability of the drive shaft in the longitudinal directionaccording to the invention is achieved by way of the drive body beingdisplaceable in the longitudinal direction of the drive shaft, and beingdriven on the cover side by way of a changing magnetic field.

Due to the cover-side transmission of the drive forces, this isindependent of an axial displacement of the drive body on pulling orpushing the shaft.

However, one may also envisage the drive shaft being connected in afixed manner to a catch body, which for its part is displaceably guidedin a direct manner in the rotor in the longitudinal direction of thedrive shaft.

In this case, the drive body is arranged in a stationary manner in theaxial direction of the drive shaft, and only a catch body which isconnected to the rotor in a rotationally fixed manner, for its part isaxially displaceable with the drive shaft. Such a catch body may forexample be designed as a body which is polygonal in cross section, forexample an octagonal body.

The invention apart from a fluid pump device of the initially mentionedtype, also relates to a method for operation of such a device, whereinone envisages the fluid pump device in the compressed condition beingbrought to a location of application, thereafter at least partlyexpanding the pump housing and thereafter displacing the pump housingand the rotor to one another in the longitudinal direction of theactuations means, in particular of a drive shaft of the rotor, such thatthe rotor is completely accommodated in the pump housing.

A greater compression of the individual parts by way of their staggeringin the longitudinal direction of the actuation means is possible withthe mentioned method steps, specifically by way of firstly theindividual elements of the pump housing, the rotor and the bearingarrangement being brought to the application location, thereafter atleast partly expanded and only after this being brought into theconstellation necessary for operation by way of relative axialdisplacement.

After the introduction of the arrangement for example into the body of apatient, with the means of the invention, one may for example retractthe drive shaft, and thus the bearing arrangement as well as the rotormay be moved in the direction of the pump housing, until the rotor islocated completely in the pump housing and is supported by the bearingarrangement as the case may be.

As to whether the rotor is expanded before or after it is introducedinto the pump housing is neither here nor there, just as is the casewith the possibility of only partly expanding the pump housing as muchas is necessary firstly before the introduction of the rotor, in orderto introduce the rotor, or whether the pump housing is completelyexpanded already before the introduction of the rotor.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is hereinafter shown and described hereinafter by way ofone embodiment example in a drawing. Thereby, there are shown in:

FIG. 1 a schematic overview of a fluid pump device, wherein the pump isinserted into a heart chamber,

FIG. 2 a three-dimensional picture of a pump rotor,

FIG. 3. a lateral view of the pump housing, of the rotor and of abearing arrangement,

FIG. 4. a lateral view of the pump housing with a rotor located therein,

FIG. 5. a detail of the pump housing in a three-dimensionalrepresentation,

FIG. 6. a bearing arrangement of FIG. 6 in a front view,

FIG. 7. the bearing arrangement of FIG. 6 in a front view,

FIG. 8. a further bearing arrangement,

FIG. 9. a bearing arrangement as from FIG. 8, in a compressed condition,

FIG. 10. a further bearing arrangement in a lateral view,

FIG. 11. the proximal end of a drive shaft with a coupling to a rotationdrive,

FIG. 12. another design of the proximal shaft end, with another couplingto a drive,

FIG. 13. an arrangement without a bearing at the distal end of therotor, in the condition staggered in the longitudinal direction,

FIG. 14. the arrangement of FIG. 13, in the operating condition, and

FIG. 15. a further development of the arrangement according to FIGS. 13and 14.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a heart chamber, which is connected to a blood vessel 2,into which blood is to be pumped. For supporting the pump activity, afluid pump 3 is introduced into the heart chamber 1, which there sucksblood and pumps this into the blood vessel 2.

A catheter 4 is introduced through a lock 5 into the blood vessel 2,through which lock the catheter may also be pulled out again. Thecatheter 4 at its distal end carries the pump 3 in the form of a pumphousing 6 connected to the catheter, and a rotor 7. The rotor 7 isrotatably mounted on a drive shaft 8 and comprises delivery elements,which on rotation suck the blood in the direction of the arrows 9 oreject it in the direction of the arrows 10 into the blood vessel 2. Forthis, the delivery elements in the shown representation, which shows theexplained position of the fluid pump, have a helically arranged deliveryblade surface.

The construction of the pump housing and the rotor will be dealt with inmore detail further below.

The drive shaft 8 runs within the catheter, which forms a sleeve in thecontext of the invention and is driven by the drive 11, which isaccommodated in a housing 12. The drive shaft thereby may form anactuation means. The drive elements are only schematically shown in FIG.1 and are explained further below likewise, in a more detailed manner.

FIG. 2 in detail shows a pump motor with two helical delivery blades 13,14, which are offset to one another by 180° on the periphery of thedrive shaft 8. The individual delivery blades consist of spanningelements such as for example struts 13 a, 13 b, as well as a frame 13 cwhich is tautened with a membrane, for example of polyurethane orpolyethylene. The frame and the struts may for example consist of amemory material which assumes its shape dependent on temperature. Thenin a compressed form at a first temperature, preferably cooled, such apump rotor may be introduced into the body of the patient and there mayautomatically unfold or expand after heating to the body temperature orsubsequent further heating.

However, it is also conceivable to automatically erect the pump rotor byway of a rotation drive in the operation direction, by way of the fluidto be delivered, thus blood in this example, catching in the deliveryblades and leading to an erection of the delivery blades by way of thecounter pressure of the fluid.

The constructional shape of the rotor may also differ from that whichhas been described above, by way of using collapsible or pivotableelements, in order to form a delivery blade surface. The pivotable partsmay then usefully be folded onto the drive shaft in the compressedcondition.

The struts 13 a, 13 b as well as the frame 13 c of the pump housing areusefully tautened, but the frame 13 c runs in the direction of the pumphousing somewhat beyond the tautening and forms a run-in chamfer there,which serves for a simpler displacement of the rotor into the pumphousing.

FIG. 3 shows a pump housing 6, a rotor 7 as well as a bearingarrangement 15, which are distributed distanced to one another axiallyon the drive shaft 8. This condition remains at least until thementioned parts are brought within a body of a patient on location.

Thereafter, the drive shaft 8 which forms an actuation means, may beretracted in the direction of the arrow 15, in order to form afunctioning construction unit of a fluid pump by way of a relativedisplacement of the rotor, pump housing and bearing arrangement.

On pulling-back the drive shaft 8, firstly the catch 17 abuts the hub 18of the bearing arrangement 15. With a continued pulling-back of theshaft, the bearing arrangement is carried along and is pressed againstthe rotor 7. This is likewise carried along and, with the continuedpulling back of the drive shaft 8, is pulled into the inside of the pumphousing 6. Thereby, the rotor 7 moves so far into the pump housing,until it is completely covered by this.

The pump housing 6 at its open end carries a fixation ring 19, in whichthe struts of the bearing arrangement 15 may clamp.

FIG. 4 shows the pump housing, the rotor and the bearing arrangement inan axially pushed-together form. The fixation ring 19 is described inmore detail in FIG. 5. It consists of two individual rings 19 a, 19 bwhich are also coaxially positioned to one another and are connected byway of connection bars which are like ladder rungs. In each case, theends of the struts 20, 21 of the bearing arrangement 15 have spacebetween the connection bars 19 c, 19 d, so that after the introduction,the bearing arrangement is radially centred there as well as axiallypositioned with respect to the ring 19. The bearing arrangement is shownschematically in FIG. 6 and comprises a hub 18 and struts 20, 21. Thestruts 20, 21 are pivotably movably fastened on the hub 18 either by wayof a joint or by way of their flexibility.

If the bearing arrangement is displaced with respect to the pump housingby way of pulling back the drive shaft, then the ends of the struts 20,21 are applied elastically into the compartments between the bars 19 c,19 d of the ring 19. There, the bearing arrangement braces automaticallyand centres the drive shaft mounted in its hub, with respect to the pumphousing 6.

FIG. 6 shows a long bearing arrangement, with which in each case asignificantly long hub piece is arranged in front of as well as axiallybehind the struts. The bearing arrangement may also be constructed in ashorter manner by way of a hub only being provided on one side of thestruts, as is shown in FIG. 8.

FIG. 7 shows a front view of the bearing arrangement of FIG. 6

FIG. 9 shows the movement ability of the struts in the compressedcondition.

On introducing the fluid pump device through a blood vessel into a humanbody, the struts 20, 21 firstly bear snugly on the hub body, as long asthe bearing arrangement is still located within the vessel, and is thenelastically expanded. This elasticity after the expansion and the axialcontraction of the pump elements ensures that the bearing arrangementremains fixed in the ring 19 of the pump housing.

FIG. 10 shows a further embodiment of the bearing arrangement with adouble shaft mounting and specifically in the region of the bearing 22,23. The struts are formed and radially extended by way of two hub parts22, 23 of the bearing arrangement approaching one another by way ofaxially pulling on the drive shaft. The struts on approaching the twohub parts are folded open on one another in a bead-like manner andextend radially away from the drive shaft. With an adequate expansion,these struts may also brace themselves in the ring 19.

FIG. 11 shows the proximal end of the shaft 8 and its coupling to adrive, which is to permit an axial displacement ability of the driveshaft by 10 to 14 mm, in order after the introduction of the individualelements of the fluid pump to the application location, to be able topull back the bearing arrangement and the rotor into the pump housing byway of pulling back the drive shaft.

FIG. 11 in this context represents a gas-tight coupling of the catheter4, which forms the sleeve for the shaft 8, onto a fluid-tight housing24. A drive body 25 is located in the housing 24 and has magnet elements26, 27 on its periphery, which on the cover side may be driven in achanging magnetic field incorporated outside the housing 24. A drivemovement is transmitted by way of this in a simple manner via thefluid-tight wall of the housing 24. For example, a second drive body 28with permanent magnets or electric magnets may rotate outside thehousing 24, or windings may be arranged there, which produce a rotatingfield.

A bolt 30 is fastened on the base 29 of the housing 24 and carries athread 31 which is stationary in the axial direction.

The rotor 25 carries a ring 32 with an inner thread which runs on thethread 31.

With a rotation of the drive body 25 in the operating direction, by wayof the cooperation of inner and outer thread, the drive body 25 is movedin the direction of the arrow 33, by which means the drive shaft 8 ispulled back. The inner ring 32 after completion of the retractionmovement of the shaft runs away from the thread 31, and as a result thedrive body 25 may rotate axially in a stationary manner. The fluid pumpis thus axially pushed together and set into operation.

FIG. 12 shows another embodiment at the proximal end of the drive shaft8. In the representation of FIG. 12, only the magnets 26, 27 of thedrive body 25 which are located within a fluid tight housing 34 arerepresented. The drive body 25 may be mounted in the housing in anaxially stationary manner and is driven in a rotational manner from theoutside. It transmits the rotation movement onto a polygonal piece 35,which is guided in a complementarity shaped opening (lock) 36 in thedrive body in a rotationally fixed manner, but axially displaceablemanner with respect to this. For example the lock 36 and the polygonalpiece 35 may be designed as a regular octagonal bolt, square bolt orhexagonal bolt.

The drive shaft 8 is connected in a rotationally fixed manner in its endregion 37 to a bush 38. An armature 39 is rotatably received in the bush38 with an undercut, and the armature does not rotate with the bush 38,but axially fixed this. The armature 39 is provided with a ring 40through which a pull tape 41 is pulled. If the armature 39 is pulledback manually in the direction of the arrow 42 by way of the pull tape41, then the armature pulls the bush 38, which may rotate with respectto the armature, in the direction of the arrow 42 a little out of thecatheter 4, so that the necessary displacements may take place in theregion of the fluid pump. The drive body 25 may be driven during thiswithout upsetting the pulling movement.

The armature 39 may be fastened in a fluid-tight manner to the housing34 by way of a bellows or a sealingly connected membrane 43, in order toensure the sealedness of the housing 34.

FIG. 13 shows a pump housing 53 which comprises a membrane which isspanned over a framework and ends in an open manner towards the distalend. The drive shaft 52 or its stiffened extension 52 is displaceddistally to the pump housing, just as the rotor 54 b. Two bearings 51,51 a are represented on the proximal side of the housing 53 and of therotor, and are axially distant to one another and provide the driveshaft or its stiffened end with a particularly stable mounting, whichalso prevents a lateral swinging-open of the unmounted end on the otherside of the bearings 51, 51 a.

Instead of two separate bearings, one may also select an individualstable and preferably long bearing on the proximal side of the rotor. Asimplified assembly and improved displacement ability with a greaterrunning stability is realised by way of this.

FIG. 14 shows the arrangement of FIG. 13 in the operating condition inwhich the shaft is pulled to the proximal end and the rotor 54 b ispulled into the housing 53.

With longer flexible shafts, it makes sense to pull the rotor withlocked bearings into the housing. In FIG. 15, the housing indentation 67prevents the shaft with the locked bearings from being pulled too farinwards. The housing indentation 68 is thus not as deep as the housingindentation 67 and permits a pulling-in of the bearing combination. Anaxial displacement of the rotor combination to the outside is no longerpossible by way of the snap-in. Bearings 64 a+b are loose on the shaft65. Locking sleeves 66 a-c are connected to the shaft in a fixed manner.

Thus in all designs, an efficient manner of the drive with adisplacement ability of the drive shaft is provided by way of theinvention, wherein the displacement of the drive shaft, for completingthe fluid pump after introduction to the place of operation, is used inan optimal manner by way of an axial relative displacement of the rotor,bearing arrangement and pump housing.

I claim:
 1. An expandable intracardiac blood pump system comprising: adrive unit; a pump housing having an open distal inflow end, the pumphousing being expandable into an expanded state and compressible into acompressed state, wherein in the compressed state the pump housing issized for percutaneous insertion into a vascular system of a patient; aradially compressible rotor disposed within the pump housing and havingat least one compressible helical blade, the radially compressible rotorhaving a proximal end section, a distal end section, and a central boreextending from the proximal end section to the distal end section; acatheter having a distal end coupled to the pump housing and a proximalend coupled to the drive unit; a drive shaft disposed within thecatheter and coupled to the radially compressible rotor, the drive shaftbeing configured to rotate the radially compressible rotor uponactuation by the drive unit; and a distal bearing assembly positioneddistal of the radially compressible rotor, the distal bearing assemblycomprising a hub and a plurality of struts pivotably extending from thehub; wherein the plurality of struts are configured to center radiallyabout an axis coaxial with the drive shaft, and wherein when theplurality of struts are expanded, the plurality of struts contact alocation along an interior surface of the pump housing.
 2. The system ofclaim 1, wherein the plurality of struts are configured to self-expandwhen the pump housing expands into the expanded state.
 3. The system ofclaim 2, wherein the plurality of struts do not rotate relative to thepump housing.
 4. The system of claim 3, wherein when the pump housing isin the expanded state, the radially compressible rotor and plurality ofstruts are also expanded.
 5. The system of claim 4, wherein when thepump housing is expanded to the expanded state, the plurality of strutsand the radially compressible rotor expand independently of each other.6. The system of claim 4, wherein the plurality of struts supports anopening in a distal portion of the pump housing.
 7. The system of claim4, wherein each strut of the plurality of struts comprises a first endsection and a second end section, the first end sections being attachedto the hub, and the second end sections comprise respective distal tipsthat extend radially away from the hub and axially away from the hub. 8.The system of claim 7, wherein the plurality of struts and the radiallycompressible rotor have respective expanded outer diameters, and theexpanded outer diameter of the plurality of struts at the second endsection is greater than the expanded outer diameter of the radiallycompressible rotor.
 9. The system of claim 4, wherein the drive shaftincludes a proximal end and a distal end, wherein the drive shaftextends through the central bore such that the distal end of the driveshaft is beyond the distal end section of the radially compressiblerotor.
 10. The system of claim 9, wherein the plurality of struts arecompressed when the pump housing is in the compressed state, and whenthe plurality of struts are compressed the hub and the plurality ofstruts are coaxial with the drive shaft.
 11. The system of claim 10,wherein when the pump housing is in the compressed state each strut ofthe plurality of struts is substantially parallel to the drive shaft.12. The system of claim 11, wherein when the pump housing is in theexpanded state the hub is coaxial with the drive shaft.
 13. The systemof claim 10, wherein when the pump housing is in the expanded state, thedistal bearing assembly centers the drive shaft radially relative to thepump housing.
 14. The system of claim 13, wherein when the pump housingis in the expanded state each strut of the plurality of struts extendsobliquely relative to the drive shaft.
 15. The system of claim 14,further comprising a knob positioned distal to the hub, the knobencapsulating the distal end of the drive shaft.
 16. The system of claim15, wherein the knob abuts a distal face of the hub.
 17. The system ofclaim 16, wherein the knob is a catch.
 18. The system of claim 4,wherein the hub has a first section that extends axially in a directiondistal to the plurality of struts.
 19. The system of claim 18, whereinthe hub has a second section that extends axially in a directionproximal to the plurality of struts.
 20. The system of claim 4, whereinthe plurality of struts expand pivotably about the hub.
 21. The systemof claim 20, wherein the plurality of struts expand about the hub by wayof flexibility.
 22. The system of claim 4, wherein the pump housingcomprises a membrane covering a framework.
 23. The system of claim 4,wherein the distal bearing assembly and the pump housing are spacedaxially apart along the drive shaft, and an axial spacing between thedistal bearing assembly and the pump housing varies during expansion ofthe pump housing into the expanded state.
 24. The system of claim 4,wherein the distal bearing assembly comprises: a first ring and a secondring, the first ring movable with respect to the second ring; andwherein the plurality of struts are disposed between the first ring andthe second ring.
 25. The system of claim 24, wherein the plurality ofstruts are configured to compress when the first ring is moved axiallyaway from the second ring along an axis coaxial with the drive shaft.